Salix linearistipularis (syn. S. mongolica) is a woody halophyte, which is distributed naturally in saline-alkali soil of Songnen plain, Heilongjiang, China. It plays an important role in maintaining ecological balance and in improving saline soil. Furthermore, S. linearistipularis is also a genetic resource; however, there is no available information of genomic background for salt tolerance mechanism. We conducted the transcriptome analysis of S. linearistipularis to understand the mechanisms of salt tolerance by using RNA-seq technology. The transcription profiles of both the salt stress (SLH-treated) and the control (SLH-control) sample for S. linearistipularis were obtained by using RNA-seq in this study. By comparative analysis, only 3034 of 53,362 all-unigenes between two samples were expressed differently at more than 1.5-fold ( $$\left| {fold - change} \right| \ge 1.5$$ , FDR ≤ 0.05), including 1397 up-regulated genes and 1637 down-regulated genes. In total, 2199 genes were classified into 50 Gene Ontology (GO) terms and 1103 genes were involved in 116 biological pathways. To find salt stress related genes, all-unigenes of S. linearistipularis were classified into three categories according to their degree of the differentially expressed genes (DEGs) at 0–1.5-fold (non differently expressed genes, N-DEGs), at 1.5–4.0-fold and more than 4.0-fold. The pathways of three categorized genes were compared with the DEGs of Arabidopsis thaliana, showing that 22, 10 and 1 pathway of S. linearistipularis were overlapped with A. thaliana. Degree of the overlapping was categorized as 0–1.5-fold, 1.5–4.0-fold and more than 4.0-folds. Our study revealed that the N-DEGs of 22 pathways in S. linearistipularis were overlapped with the DEGs of A. thaliana. This result suggests that those overlapped genes that contrasted with the up- or down-regulated genes in A. thaliana were possibility evolved into housekeeping genes in S. linearistipularis under salt stress.

Drought stress is one of the most prevalent abiotic stressors and severely impairs plant growth and productivity. Therefore, identifying functional genes associated with drought tolerance is essential for the molecular breeding of drought-resistant crops. The RD22 (Responsive to Desiccation 22) gene family encodes conserved BURP domain-containing proteins that participate in plant responses to drought stress. In this study, two RD22 homologs, DsRD22a and DsRD22b, were isolated and characterized from the drought-tolerant ornamental species Dianthus spiculifolius. Sequence analysis showed that both proteins contain a conserved BURP domain and are typical members of the RD22 family. Tissue-specific expression analysis revealed that both genes were predominantly expressed in leaves and stems. Abiotic stress assays demonstrated that the expression levels of DsRD22a and DsRD22b were significantly induced by abscisic acid (ABA), osmotic stress, and salt stress, whereas their transcriptional responses to relatively low-temperature and oxidative stress were relatively weak. Subcellular localization analysis indicated that DsRD22a and DsRD22b proteins are localized in the cytoplasm. Heterologous overexpression assays showed that transgenic Arabidopsis thaliana lines overexpressing DsRD22a or DsRD22b exhibited significantly enhanced tolerance to salt and osmotic stresses compared with wild-type (WT) plants. Soil drought assays further confirmed that the transgenic lines had higher soluble protein contents and improved drought tolerance than WT plants. These findings suggest that DsRD22a and DsRD22b positively regulate plant responses to drought stress, potentially by promoting soluble protein accumulation. Collectively, DsRD22a and DsRD22b represent valuable candidate genes for the genetic improvement of drought tolerance in plants.